keys to spray drift management robert e. wolf extension specialist application technology biological...
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Keys to Spray Drift Management
Robert E. Wolf Extension Specialist Application Technology
Biological and Agricultural Engineering
Accurate and Efficient Applications
Increase Efficacy
Minimize Drift
Maximize Productivity
Coverage/Drift:
Need knowledge of the product being used.
Herbicide, Fungicide, Insecticide• Systemic• Contact
Uniform coverage.What is the target?
• Soil• Grass• Broadleaf (smooth, hairy, waxy)• Leaf orientation – time of day• Penetration into canopy
Why Interest in Drift?
Spotty pest control Wasted chemicals Off-target damage More high value specialty crops Urban sprawl and..... Less tolerant neighbors Litigious Society More wind?? (Timing) Environmental impact
• Water and Air Quality Public more aware of pesticide
concerns! (Negative) (Perceptions) Result-higher costs-$$$
Plant Response1/100 Rate of 2,4-D Simulated as Drift
14 Days After Exposure
5 30
80
20
0
10
20
30
40
50
60
70
80
90
100
Cherry Grape Cotton Pea
Per
cent
inju
ry
Kassim Al-Khatib - Kansas State, Cal Davis
Cotton Response1/100 Rate 2,4-D Simulated as Drift
14 Days After Exposure
80 80
60
40
25 20 150
102030405060708090
100
Per
cent
inju
ry
Kassim Al-Khatib - Kansas State, Cal Davis
Technical Aspects of Spray Drift
Definition of Drift:
Movement of spray particles and vapors off-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people.
Adapted from National Coalition on Drift Minimization 1997 as adopted from the AAPCO Pesticide Drift Enforcement Policy - March 1991
Types of Drift:
Vapor Drift - associated with volatilization (gas, fumes)
Particle Drift - movement of spray particles during or after the spray application
Factors Affecting Drift:
Spray Characteristics chemical formulation drop size evaporation
Equipment & Application nozzle type nozzle size nozzle pressure height of release
Weather air movement (direction and
velocity) temperature and humidity air stability/inversions topography
Efficacy and Drift Mitigation:
Size of the Spray Droplets - MicronsVolume Median Diameter (VMD)
Droplet Spectrum (Range - big to small)
% Volume in droplets less than 200 microns in size
One micron (m) =1/25,000 inch
Drop Size:
Comparison of Micron Sizes for Various Items: (approximate values)
pencil lead 2000 (m)
paper clip 850 (m) staple 420 (m) toothbrush bristle 300 (m)sewing thread 150
(m)human hair 100 (m)
150
1/2 of spray volume = larger droplets
VMDVMD
1/2 of spray volume = smaller droplets
Important Droplet Statistics:
Operational Area
Droplet measurement terms:
VD(0.1) – droplet diameter where 10% of spray volume is smaller (90% is greater)
VD(0.9) – droplet diameter where 90% of spray volume is smaller (10% is greater)
Relative span (RS) – used to describe the “width” of the spectrum
VD(0.9) – VD(0.1)RS =
VMD
Relative Span
RS = (Vd.9 – Vd.1)/VMD
Vd.9 = 500, VMD = 300, Vd.1 = 200
Vd.9 = 700, VMD = 300, Vd.1 = 100
Nozzles Types?
The CP STRAIGHT STREAM NOZZLE
Weather factors of concern:
air movement (direction and velocity)
• Topography, etc. temperature and humidityair stability/inversions
Cloud of 5-25 u oil droplets generated under unstable conditions
105 foot temperature monitoring tower
8’ 41°F
16’ 41°F
32’ 40°F
64’ 40°F
105’ 38°F
Courtesy – George Ramsay, Dupont
Wind direction:
Wind direction is very important• Know the location of sensitive
areas - consider safe buffer zones.• Do not spray at any wind speed if it
is blowing towards sensitive areas - all nozzles can drift.
• Spray when breeze is gentle, steady, and blowing away from sensitive areas.
• “Dead calm” conditions are never recommended.
Determining wind direction:
Compass• Provide magnetic
description• Direction blowing from• Into your face!
Drift Potential: High at Low Wind Speeds?
Because:• Light winds (0-3 mph) tend to
be unpredictable and variable in direction.
• Calm and low wind conditions may indicate presence of a temperature inversion.
Drift potential is lowest at wind speeds between 3 and 10 mph (gentle but steady breeze) blowing in a safe direction.
Wind Speeds: Spray Droplet Movement
Droplet Sizes (microns)
5 mph Wind
10 mph Wind
15 mph Wind
20 mph Wind
100 24 ft. 48 ft. 72 ft. 96 ft.
200 9 18 26 35
400 5 9 14 18
500 4 7 10 14
600 3
6 9 12
Boom height: 3 feet
Wind Speeds Gradients:
The relation between height above the canopy of a crop like cotton or soybean and the speed of
wind.
30
20
10
6
2
0
11 mph
10 mph
8 mph
7 mph
5 mph
Hei
gh
t A
bo
ve C
rop
Can
op
y, F
eet
Wind Current Effects:
Wind currents can drastically affect spray droplet deposition
Structures drastically affect wind currents• Wind breaks• Tree lines and orchards• Houses and barns• Hills and valleys
Wind Patterns Near Treelines:
Adapted from Survey of Climatology:Griffiths and Driscoll,
Texas A&M University, 1982
Wind Patterns Around Buildings:
Diagram of wind around a building.Adapted from Farm Structures*
Ground
* H.J. Barre and L.L. Sammet, Farm Structures (Wiley, 1959)
Handheld windmeters:
On board weather instrumentation:
Aventech Research Inc.• Aircraft Integrated Meteorological
Measurement System –AIMMS AIMMS-10 AIMMS-20
Air flow probe 2 - measurement modules CPU (20 second updates)
Wind speed and direction transmitted on-board• Used and logged• PDA software available for real
time display of meteorological conditions.
http://www.aventech.com
On board weather instrumentation:
www.ambientweather.com/handheld.html
Under normal conditions air tends to rise and mix with the air above. Droplets will disperse and will usually not cause problems.
Normal Temperature Profile
Altitude
Cooler
Warmer
Temperature decreases with height
Increasing Temperature
Inversions:
Under these conditionsthe temperature increases as you move upward. This prevents air from mixing with the air above it. This causes small suspended droplets to form a concentrated cloud which can move in unpredictable directions.
Temperature Inversion
Altitude
Temperature increases with height
Warm Air
Cool Air
Increasing Temperature
Temperature Inversions:
Cloud of 5-25 u oil droplets generated under unstable conditions
105 foot temperature monitoring tower
8’ 41°F
16’ 41°F
32’ 40°F
64’ 40°F
105’ 38°F
8’ 33°F16’ 36°F32’ 37°F64’ 38°F
105’ 38°F
.5 mph wind
2.5 mph wind
Shallow surface inversionSTABLE conditions up to 64’ NEUTRAL conditions at 105’
Cloud is dispersing
Courtesy – George Ramsay, Dupont
Recognizing Inversions:
Under clear to partly cloudy skies and light winds, a surface inversion can form as the sun sets.
Under these conditions, a surface inversion will continue into the morning until the sun begins to heat the ground.
Precautions for Inversions:
Surface inversions are common . Be especially careful near sunset
and an hour or so after sunrise, unless…• There is low heavy cloud cover• The wind speed is greater than 5-6 mph
at ground level• 5 degree temp rise after sun-up
Use of a smoke bomb or smoke generator is recommended to identify inversion conditions.
Evaporation of Droplets:
Wind
High Relative HumidityLow Temperature
Low Relative HumidityHigh Temperature
Fal
l Dis
tanc
e
Strategies to Reduce Drift: Select nozzle to increase drop size Increase flow rates - higher application volumes Use lower pressures Use lower spray (boom) heights Avoid high application speeds/rapid speed changes Avoid adverse weather conditions
• High winds, light & variable winds, calm air Consider using buffer zones Consider using new technologies:
• drift reduction nozzles• drift reduction additives• shields, electrostatics, air-assist, pulse width
modulation
Drift Reduction Additives:
Many available! Not EPA regulated Long chain polymers Soluble powders 50 - 80% reduction in off-
target movement Not all will work!!!! Pump shear problems Effect on the pattern?
EPA Requested Changes on the label
Guidance to Chemical Manufacturers
Better information on the label for applicators on mitigating drift.
Match crop protection products to target.
Adopt droplet standard (1999)• ASABE S-572
Buffer Zones or No Spray Zones Maximize Efficacy - Minimize Drift
Example Reference Graph
Cumulative Volume Fraction
0.1 0.5 0.9D
rop
Siz
e (m
icro
ns)
0
100
200
300
400
500
600
700
800
900
very fine/ fine fine/mediummedium/ coarsecoarse/ very coarsevery coarse/ extremely coarse
VF
F
M
CVC
XC
Drift Reduction Technology Program – DRT (2006)• Encourage the adoption of technology designed to reduce
drift.• Use of a testing approach to generate high quality peer-
reviewed data for DRT’s, including test design and quality assurance (QA).
Example technologies:• Spray nozzles – reduce fines• Sprayer modifiers – shields, hoods• Spray delivery assistance – air-assist• Spray property modifiers – formulations, drift control• Landscape modifications – hedges, shelterbelts
EPA’s New Emphasis with Spray Drift Reduction
Distance from application site
Am
ount.
of
dri
ft a
nd
risk
Level of concern for a pesticide for people, animals, plants
No DRTDRT* DRT**DRT ***
Relationship Between Application Technologies, Amount of Drift/Risk, and Risk
Management
http://www.ksda.gov//
In Conclusion:
Minimizing spray drift is in the best interests of everyone. Do your part to keep applications on target.
Disclaimer:
Brand names appearing in this presentation are for identification and illustration purposes only.
No endorsement is intended, nor is criticism implied of similar products not mentioned.
